April 20 is World Marijuana Day.

It's just over two years since Jamaica decriminalised small quantities. And Canada was set yesterday to announce what's likely to be a bolder experiment.

So what has changed, and what hasn't?

The big change in Jamaica is for small-scale users. Possession of up to two ounces is no longer a criminal offence. You can grow up to five plants at home. And smoking in public is a minor matter, with a fine equivalent to TT$25.

For perhaps a few hundred-thousand Jamaicans those reforms make a huge difference. They remove the daily risk of arrest, prison, a substantial fine—and a criminal record which blocks some employment or a US visa.

Mario Deane was beaten in a police cell in August 2014, and died three days later. He was a 31-year-old construction worker, arrested with one spliff of ganja, and awaiting bail. That was six months before the law changed.

Three police officers were charged with manslaughter, misconduct and perverting the course of justice. That case has been tied up in a parish court for close to two years. Whatever the verdict, Mario will stay dead.

But there will now be fewer Marios.

Ganja has become respectable. Last month, the tourist centre of Negril hosted a Stepping High Ganja Festival. For Marijuana Day next week, the University of the West Indies plans a symposium, with national awards in six categories.

What has not changed is the supply chain. Growing commercial quantities for recreational use is still illegal. So is selling it. The ganja trade is still controlled by murderous criminal gangs. Turf wars continue.

The retail price has not changed. It's still the equivalent of up to TT$5 for a bag.

Exporting remains illegal. On Monday this week, a 41-year-old telecoms engineer from London was held at Norman Manley International Airport with 28 pounds of ganja.

Last year, the Narcotics Division made around 800 arrests. Mules were held en route to T&T, Barbados or Curaçao—from where there's a lively return trade in cocaine. Others were booked on flights to London or North America.

And what is about to change?

Since last year, a Cannabis Development Authority has accepted 190 applications for licences to grow, transport, process or sell medical marijuana.

Licensing is a slow and careful process. Applicants are vetted to weed out those with a criminal record or other stain. Systems must be in place to secure the crop. There is software to tag and track each plant from field to the point of sale.

So far, three conditional licences have been granted.

An alternative development programme will allow existing small growers to transition to licensed cultivation.

There are plans for airport kiosks, where tourists will buy permits for medical marijuana.

Jamaica needs to stay cautiously with what's allowed under the UN's 1961 narcotics convention—signed by Britain one year before Jamaican independence. The UN still classifies marijuana up there alongside heroin.

There are dissenters. The National Council on Drug Abuse reports a 50 per cent increase since decriminalisation in children requiring treatment for ganja-related troubles. Toddlers have been brought to hospital comatose after finding and eating marijuana sweets or cookies. The health minister, Christopher Tufton, backs the council.

Jamaica's chief medical officer—who is a psychiatrist—says one in every ten adult ganja users will become addicted; as will half of all adolescents who try the drug. He says that ganja is responsible for 90 per cent of teenagers with behavioural problems or at suicide risk.

There were ganja-related medical problems before decriminalisation. But parents and teens can now seek medical advice more openly.

And Canada? Easing up on recreational ganja was in Justin Trudeau's election manifesto. Target date is July 1, 2018—Canada Day. Up to yesterday, there was still plenty to decide—age limits, whether to sell in pharmacies or liquor stores, advertising and packaging restrictions. Many of these issues will be left to the provinces. Nationally, drugged driving remains a tough question.

Big companies are involved. Seven are lobbying for commercial branding and marketing. There are plans for large-scale commercial cultivation. One producer is building an 800,000 square foot facility in Edmonton.

As the world's tenth-largest economy, Canada is well placed to deal with international pressure over the 1961 convention.

There are worries; CBC reports that organised crime has infiltrated the thriving medical marijuana business. If the tax rate is set high, criminal supply chains will continue to dominate recreational marijuana after liberalisation.

Canada has technology and scale. Jamaica offers cultural history. Marley Natural cannabis products launched this month in Washington state—though under current restrictions ganja can't be grown in Jamaica and exported.

At worst, the outcome for Jamaica could be like the story of Blue Mountain coffee—a well established brand, but a tiny, ramshackle production sector.

And why April 20? There's a bunch of stories. The most credible links to a defunct California police code “420” which signalled “marijuana smoking in progress.”

That sounds more North American than Jamaican. Marijuana Day may not be good news for Caribbean growers.